This disclosure relates to the preparation of reactive, friable polyimides. Polyimides, which include polyetherimides, are thermoplastic polymers with a number of desirable properties such as high strength, high toughness, excellent chemical resistance, and high temperature stability due to a high glass transition temperature. They are typically high viscosity materials and the high viscosity combined with the high glass transition temperature can hinder the use of polyimides, particularly polyetherimides, in blends, composites, and coatings.
Polyimides can be added to thermoset composites. Reactive friable polyimide powders are desired to facilitate incorporation into the composite matrix. Reactive friable polyimide powders having molecular weights of about 40,000 to about 80,000 g/mole and a particle size of 100 micrometers or larger are described in U.S. Pat. No. 6,713,597. The higher molecular weights translate to a high viscosity which has a negative impact on incorporation of the polyimide into the matrix. Reduction of particle size is by milling, for example jet milling, which subjects the particles to a pressurized stream of gas and particle size is reduced by interparticle collisions. Accordingly, there is a need in the art for a low molecular weight, highly friable polyimide powders, in particular powders that can be size reduced by simple mechanical grinding.